Heavy Wind

[sailbadthesinner]

Re: but what about

ooh i am getting all confused now
jimi was right pressure is the force exerted by the atmosphere which naturally takes account of the content of the atmosphere at that point.

Is cold air denser than warm air was the question. i got confused by thinking cos warm air could potentially suspend more water vapour due to greater absolute humidity potential greater then it is potentially denser

what i was really working to was that the only dense thing for miles around is me.and i should get back to work.
.

<hr width=100% size=1><font color=red>I can't walk on water, but I do run on Guinness</font color=red>

 

[tcm]

Re: Light Water

Clouds float for the same reason that feathers floats - their very small size makes their movement in air more dependent on updrafts and less dendent upon gravity. As they grow, then they become more affected by gravity, and behave less like feathers.

I imagine that most would be happier to have their sail impelled by air moving at 20 knots than by a wall of water moving at the same speed. Colder and damper air is denser.


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[sailbadthesinner]

Re: just as well ...

you still tryin to hawk those old puns around here
you must stop
eider one way or another

<hr width=100% size=1><font color=red>I can't walk on water, but I do run on Guinness</font color=red>

 

[Twister_Ken]

WRONG!!!!

Tee-hee. This got me Googling. How do you like the quote...

"So, dry air weighs more than moist air, which is why clouds can exist where they do, seeming to 'float' across the skies"

Taken from the US national weather service website at <A target="_blank" HREF=http://www.wrh.noaa.gov/Flagstaff/science/cloud.htm>light is right</A>

Counter-intuitive, innit?

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[Twister_Ken]

Re: just as well ...

Stop sniping and get back to work!

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[jimi]

Re: just as well ...

Ah'll bet Ross ten starling that Robin'll eaglely wrender the gullible by thrushing and then ostrichising 'em!

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[AndrewB]

Oops - you\'re quite right!

That's the trouble with being a newbie, I can't interpret my own formulae correctly.

Density = Air Pressure /(Adjusted Temperature x 2.87)

So as air pressure increases, the density increases. As the adjusted temperature rises with increased relative humidity, the density falls.

The site you found conveniently provides the formula for temperature adjustment <A target="_blank" HREF=http://www.usatoday.com/weather/wvirtual.htm>here</A>.

So .... when the pressure is 1030 mb, the temperature 0C, and the RH is 30%, air density is 1.31 Kg per cu m. When the pressure is 970, the temperature 30C and the relative humidity 100%, air density is 1.10 Kg per cu m.

In other words, the cold, dry, high-pressure day has an air density 20% higher than the warm, wet, low-pressure day, and equivalent windspeeds exert 20% more pressure on the yacht.

Hope I've got it the right way round this time!

 

[ean_p]

Re: Oops - you\'re quite right!

my head hurts.........

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[TheBoatman]

Re: Newbie-ish calculation

Andrew,,,you just blew the fuse in my brain,, thanks mate!!!

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[vyv_cox]

Re: Oops - you\'re quite right!

I'm OK with this right up to your last clause of your next-to-last sentence. All the calculations that you have kindly done for us refer to air pressure, that is the weight of atmosphere that is pressing down upon us. I'm not at all sure that this makes a difference to the "weight" of the wind because it is all relative. Wind on a warm, wet day is warm and wet, whereas wind on a cold dry day is cold and dry.

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[Twister_Ken]

Why is moist air lighter?

Could it be because nitrogen and oxygen atoms (atomic weight 14 and 16 respectively), are being displaced by water molecules (total atomic weight 18 for the 3 atoms of H20, or avg atomic weight 6)?

Any chemists out there?

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[claymore]

Re: Why is moist air lighter?

Not a Chemist but there was some pretty heavy stuff flying around Tobermory Harbour last weekend and it was quite moist too.
Hope this helps

<hr width=100% size=1>regards
Claymore
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[AndrewB]

No ... its WIND pressure

... that these calculations relate to. Wind pressure on the yacht is directly proportional to air density for given wind speed. That's if the website I cited in my first post can be believed (<A target="_blank" HREF=http://www.knmi.nl/samenw/hydra/faq/press.html>Check here</A>).

Actual rain would present a different situation. PLEASE don't ask me to calculate that!

 

[tcm]

Re: Why is moist air lighter?

Ooh. Was the rain falling upwards as per ken's chemistry calculations, and did all the morning mist naff off into outer space? I'm getting lost now. However, if you leave a boat damp inside, it's the things on the floor that go manky, whilst things higher up near the roof are nice. So, I disagree that moist air is lighter. Cos it has water droplets innit, innit, as a liquid, which is 1000g/litre unlike air which er is much less.

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[tcm]

Excellent idea

Except er that would mean all the now-lighter-than air seawater would be floating above the recently-discovered-to-be-heavier air below it, with nasty repercussions. You would need a space suit for sailing, thee engine wouldn't work cos no air, and sinking would involve falling down through the water, and then an 11miles drop and crunch to the earth's surface.

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[claymore]

Re: Why is moist air lighter?

Too deep for me - I'll bow to obviously superior knowledge, leaving you with this single observation that the water always stays in the bog and its always wet and its always screwed to the floor as opposed to the ceiling. So that must tell us something mustn't it?
Anyway - off now, intellects to massage, brains to find. Friday afternoon teaching is great - we enjoy the common bond of not wanting to be there - its an emotional time for us all. I feel we are on the crest of a slump here.

<hr width=100% size=1>regards
Claymore
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[Twister_Ken]

What a gas

Ah, but water is a liquid (or a solid if it cold enough), whereas water vapour is a gas.

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[DeeGee]

Re: Why is moist air lighter?

Moist air is not lighter than dry air.
I used to know all about this stuff, but have forgotten the last line...

The reason why clouds form goes like this...
Air is heated by warming of the ground by the sun. Hot air rises (not like on SB). Now, as we all know, it gets colder as you go up in the atmosphere. You might expect this bubble of hot air to just keep going up, which it does. However there is a thing called the adiabatic lapse rate which looks at the way it expands and since there is no interchange of heat with the surroundings, it therefore gets colder internally. It does this faster than the drop in ambient air temperature so it will stop going up when the bubble temperature is the same as the ambient air temperature. This drop in temperature means that the moistness starts to turn into visible water vapour (steam=clouds). What I can't remember is why it doesn't just turn into rain at that point and fall out of the sky. I do remember that minute particles like diesel soot are required to start a rain-drop. Maybe someone can finish the explanation?

<hr width=100% size=1>Black Sugar - the sweetest of all

 

[tcm]

Re: ah but erm

the water vapour is air, with some water droplets in. The water droplets are shirley heavier than the air. They aren't gaseous H's and O's, otherwise you could boil some water and kerbang blow the house up with hydrogen and oxygen. Anyway, you're still not having my bunsen burner, I bet this won't come up in the exam. Or did it?

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[tcm]

Re: yes yes

the teensy droplets of water flutter around like feathers or dust, the effects of updraughts and wind affecting them more than gravity. And dust doesn't kerunch hit the groiund does it, ules it was a great slug of dust.

So any, with some dust arriving on the scene, the positively (or er negatively ) charged droplet are attracted to the dust building into a bigger droplet, whichthen falls, cos it is heavy enough. Unless there's a massive updrught in which case it rises, freezes, falls, rises again and gets bigger and comes down as hail.

Also, in america they chuck stuff into the air to make it rain.

I think we've tackled this question very well realy, and should get a B.


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